Variable electrical resistor



Jan. 22, 1957 J. R. ALTIERI VARIABLE ELECTRICAL RESISTOR 2 Shets-Sheet 1 Filed Oct. 19. 1954 w. w 40 M a 6 3 W WZw w i; Z 6 v 4W7 7 T a .1 owltfifl t gm: 0 X 1 3 M Z wf. mm 3 4 a 4 9 w 3 2 0 M 34 4 4 4.

Jan. 22, 1957 J. RHALTIERI 2,778,908

VARIABLE ELECTRICAL RESISTOR Filed Oct. 19. 1954 2 Sheets-Sheet 2 :W' W," {W

United States Patent VARKABLE ELECTRICAL RESISTOR Joseph R. Altieri, Watertown, Mass., assignor to Acton Laboratories, Inc., Acton, Mass.

Appiication October 19, 1954, Serial No. 463,222

4 Claims. (Cl. 201-56) The present invention relates to variable electrical impedances, and more particularly to electrical impedances having rnultiturn rotary impedance changing elernents.

In recent years, a need has developed for variable electrical impedances which may be varied throughout their range by rotation of an impedance changing element a plurality of turns. The single turn electrical impedance which has been conventional in the art has been found to be unsatisfactory for certain applications, either because it' failed to provide sufficient space for the resistive element to permit the dissipation of relatively large powers, or because the variable resistor was to be coupled to an electrical motor and driven throughout its range over a relatively long period of time.

The rnultiturn variable resistors which have heretofore been available in the art have been subject to certain disadvantages which are overcome by the present invention. In order to provide rnultiturn operation, it is necessary to provide a contact with the resistive element which is not directly attached to the shaft of the variable resistor but is coupled to the shaft through a turn multiplying device. One construction which permits multiple turn operation is to mount a threaded shaft to a support and mount the contact upon a traveling nut disposed upon the threaded shaft. The nut is keyed to the support, so that rotation of the threaded shaft causes the traveling nut to move the contact across the turns of a helical wound resistance element which is attached to the support.

Mechanically this structure has a disadvantage in that the threaded shaft is journaled at both ends in order to obtain axial alignment. Electrically, the structure also has a disadvantage in that the resistance of the variable resistor is varied in step units as the contact slides from one turn to another.

It is an object of the present invention to provide a variable resistance multiturn device in which the resistance is continuously variable throughout the range of the device.

It is a further object of the present invention to provide a variable rnultiturn resistor having a rotatable element which is journaled within only one wall of the supporting structure.

It is also an object of the present invention to provide a rnultiturn variable resistor in which the rotatable element is journaled within only one wall of the supporting structure in which slight misalignment of the rotatable element relative to the supporting structure can be tolerated.

Other objects and advantages of the present invention will become readily apparent from a further reading of the present disclosure, particularly when viewed in the light of the drawings, in which:

Figure 1 is an end elevational view of the container of a rnultiturn resistor constructed according to the teachings of the present invention, the end cover and rotatable element being removed;

Figure 2 is a sectional view of the resistance element of the multiturn resistor taken along line 22 of Figure 1;

Figure 3 is a vertical sectional view of the rotatable element of the multiturn resistor, partly shown in elevation;

Figure 4 is an enlarged fragmentary sectional view of the rotatable element illustrated in Figure 3;

Figure 5 is a vertical sectional view of the resistance element disposed about a mandrel during the process of manufacture;

Figure 6 is a sectional view taken along line 66 of Figure 5; and

Figure 7 is an enlarged fragmentary view of a portion of the resistance element.

As illustrated in the figures, the rnultiturn variable resistor is constructed with a helical resistance element 10 disposed about a contact 12. The contact 12 is attached to a rotatable element 14 which is journaled within a cover 16 of a container 18 for the rnultiturn variable resistor. The container 18 has a cylindrical sleeve 20 which contains the helical resistance element 10. The cover 16 of the container 18 is disposed at one end 22 of the cylindrical sleeve 21), and a dust cover 24 is disposed at the opposite end of the cylindrical sleeve 20.

The helical resistance element 19 is constructed with a continuous winding 26 of resistance wire about a relativeiy flexible strip 23 of electrically insulating material. The helical resistance element It) is disposed within a cylinder 3 of electrical insulating material, the cylinder 3% being disposed adjacent to the cylindrical sleeve 26 of the container 13. A thin layer 32 of adhesive electrically insulating material, such as permaiill, is disposed between the cylinder 3i) and the cylindrical sleeve 20 of the container 18, and also between each turn 34 of the helical resistance element it? and the cylinder 30, this layer being designated 36. The layer 36 of permafill also serves to separate and electrically insulate the turns 34 of the helical resistance element 10 from each other.

The helical resistance element 10 is formed by winding the turns 34 thereof on a mandrel, designated 38 in Figures 5 and 6. The layer 36 of perrnafill is then applied to a fiat sheet which is wrapped around the turns 34 of the helical resistance element 10 to form the cylinder 30. The layer 32 of permafill is then placed upon the cylinder 30, and the entire assembly including the mandrel 38, resistance element 1t cylinder 30, layers of permafill 32 and 36, are then slipped within the cylindrical sleeve 20 of the container 18. The assembly is then placed within an oven and baked to harden the permafill which then becomes an effective electrical insulator which is moisture-proof and fungus-proof and capable of withstanding relatively high temperatures. Figure 5 illustrates the assembly in condition for baking.

The rotatable element 14 is illustrated in Figures 3 and 4, and is journaled within the cover of the container 3.3. A threaded sleeve 4% extends through the cover 16 for the purpose of attaching the rnultiturn variable resistor to a panel, or the like. The sleeve 40 is provided with a flange 42 adjacent to the inner surface of the cover 16. Beyond the flange 42, the sleeve 4d continues as a threaded screw 39. Figure 4, the threaded portion 3'9 is provided with an axial bore 44 which extends therethrough, and a shaft 46 is rotatably disposed within the bore 44. A ring bearing 48 is press fitted into the bore 44 adjacent to the inner end of the screw 39, and the shaft 46 is journaled within the ring bearing 48. The shaft 46 extends through the ring bearing 4-8, and a lock washer 58 is attached to the shaft adjacent to the ring bearing in order to prevent the withdrawal of the rod 4-6 through the cover 16. A second lock washer 52 is attached to the shaft 46 adjacent to the end of the sleeve 40 to prevent the As illustrated in.

apropos shaft 46 from slipping further into the container 13. A split ring 54 surrounds the shaft 46 adjacent to its end, and the split ring 54 is held firmly attached to the shaft 46 by a tapered collet 56 adjacent thereto. A ring 58 adjacent to the tapered collet 56 is provided with a conical shaped side 60 which abuts the tapered collet 56. Lock screws 62 extend through apertures 64 in the ring scans are threaded into a base ring 66 which is disposed adjacent to the end of the threaded screw 39 and spaced therefrom. The pressure exerted by the ring 53 against the tapered collet 56 wedges the split ring 54 against the shaft 46 when the lock screws 62 are tightened into the base ring 66, so that the base ring 66 is securely attached to the shaft 46. A ring of electrical insulation 68 is disposed about the periphery of the ring 58 and separates a grooved electrically conducting ring '79 from the ring 58. The ring 79 is electrically connected to the contacts 12 by an insulated wire 72.

A cage 73 is attached to the base ring 66 at one end and is slidably disposed about the flange 42 at the other end. As a result, rotation of the shaft 46 rotates the cage 73 relative to the screw 39. The cage 73 is provided with a slot '74 which extends from the flange 42 to the ring 66 and is parallel to the axis of the bore 44 in the screw 39. A traveling nut 76 is threaded upon the screw 39 and is provided with a protruding portion 78 which extends through the slot 74 in the cage 73 to key the nut 76 to the cage 73. The contact 312 is mounted to the traveling nut 76 the traveling nut being constructed of electrically insulating material, such as polyethylene plastic. The wire 72 connects the contact 12 to the ring 7%. A plurality of apertures 86 are disposed in the cage 73 to reduce the weight of the cage 73.

7 When the rotatable element 14 is disposed within the cylindrical sleeveib of the container 13, the cover 16 is sealed to the end 22 of the container 13. The contacts 12 are then abutting one of the turns 34 of the helical resistance element 19 and contact to this turn is made to the electrically conducting ring 70. The contacts 12 comprise a pair of precious metal alloy members 71 which are constructed of resilient metal to provide a spring Contact to the resistance element 1% Due to this fact, slight misalignment of the rotatable element 14- within the container 18 will not prevent the contact from resting upon the turns of the resistance element 16.

The groove in the electrically conducting ring 70, designated 82, accommodates a pair of spring contacts 84 disposed upon opposite sides of the ring '76. The spring contacts 84 are electrically connected to one terminal 86 of a three terminal connector strip 88 affixed to the exterior surface of the cylindrical sleeve 20 of the container 38 adjacent to the dust cover 24. The terminal strip 88 is provided with a strip 9i) of electrically insulating material upon which are mounted three terminals 86 in spaced insulated relationship with each other. The other two terminals 86 are connected to the ends of the helical resistance element 10, the conductors therefor being disposed within channels 92 extending through the cylindrical sleeve 2! of the housing parallel to the axis thereof and adjacent to the insulating cylinder 30.

The dust cover 24 is applied to the cylindrical sleeve 2t) of the container 18 to seal the container 13. In the particular embodiment described, the container 18 is constructed of aluminum, which provides an accurate support for the resistance winding 26. The resultant structure is capable of withstanding high operating tem peratures.

It is clear that the contacts 12 continuously ride upon the turns 34 of the helical resistor element and provide continuous resistance variation throughout the range of available resistance. It is also apparent that the rotatable element 14 within the container 12 is journaled in only one location, eliminating the necessity for aligning the rotatable element with two separately disposed bearmgs.

Figures 5 and 6 show certain details of the mandrel 33 used securing the resistance element 34 in the cylindrical housing 26. The mandrel consists of a cen tral member having a square cross-section portion 41 having at each end a cylindrical portion 43 followed by reduced diameter threaded portions 45 and terminating in smaller cylindrical portions 47. Positioned on the top and bottom of the square central portion 41 are two similar arcuate portions 9 and 51, and at the right and left complementary to these portions are other arcuate portions 53 57 as may be seen from Figure 6. All of the portions 49, 51, 53 and 57 are provided with an annular rim portion 59 at each end. The annular portion 59 at the left end of the structure shown in Figure 5 engages an annular groove in a retaining member 61 having a larger annular groove 63 for engaging the periph eral portion of one end of the cylindrical housing 2%. A suitable hand nut 65 bears against the left end surface of the retaining member 61.

The annular portion 59 at the right end of the arcuatc segments 49, 51, 53 and 57 fits into an annular groove in a retaining member 67, which at the right end bears against a hand nut 69 mounted on the threaded portion 45. Thus the various segments are retained in position for winding the mandrel with the resistance element 34 by these members prior to insertion into the cylindrical housing 2%. After the insulating material 39 has been applied to the helical winding and cement applied to the exterior of the member 30, the cylindrical housing 20 is slipped over the assembly. Thereafter the nut 69 may be removed and a further retaining member positioned as shown in Figure 5 so that the entire assembly may be accurately supported on the cylindrical stud ends 47 in an oven for baking.

After the device has been baked the right hand nut 69 is removed, and the two retaining members 67 and 75 removed. Thereupon it is usually possible to withdraw the square central portion 41, whereupon the arcuate pieces 53 and 59 may be removed, and thereafter the arcuate pieces 4 and 51. The use of the mandrel assures that the inner surface of the resistance element 34 has a true cylindrical configuration. This method furthermore has the advantage of assuring that the resistance strip is bonded to an accurate inner cylindrical surface providing good heat conductivity so that the potentiometer will be operated at temperatures considerably elevated above those of more conventional construction.

The man skilled in the art will readily see many other uses and advantages of the present invention in addition to those set forth in the present disclosure. For this reason, it is intended that the scope of the present invention be not limited to the specific embodiment herein described, but rather only by the appended claims.

What is claimed is:

1. A variable multiturn resistor comprising a container having a cylindrical sleeve and a cover at one end of the sleeve, a helical screw disposed on the axis of the sleeve and attached to the cover, said screw being provided with an axial bore extending thcrethrough, a shaft rotatably disposed in the bore of the screw, a cylindrical cage provided with a slot parallel to the axis thereof rotatably and concentrically disposed about the screw, means to couple the cage to the shaft, a traveling nut rotatably mounted on the screw and having a protruding portion slidably disposed within the slot in the cage, a helical coil comprising a fiat ribbon of electrically conducting material mounted to the interior of the container approximately concentric to the screw, a spring electrical contact mounted to the traveling nut in slidablc contact with the helical coil, said shaft extending through the mouth of the bore remote from the cover, the means for coupling the cage to the shaft comprising a split ring disposed about the portion of the shaft exterior to the bore, a tapered collet surrounding the split ring, a ring having a tapered aperture therein confronting the tapered surface of the tapered collet disposed about the collet, a base ring disposed adjacent to the tapered ring and attached to the end of the cage, and means to draw the tapered ring to the base ring thereby wedging the split ring to the shaft.

2. A variable multiturn electrical resistor comprising the elements of claim 1, in combination with a ring of electrically insulating material disposed about the periphery of the tapered ring, and a ring of electrically conducting material disposed about the periphery of the electrically insulating ring, said electric.-'1ll', conducting ring being provided with a peripheral groove thereabout and being electrically connected to the electrical contact upon the traveling nut, 21 pair of spring electrical contacts mounted to the casing and slidably disposet with in the groove in the electrically conducting ring, whereby electrical connection with the electrical contact may be obtained at the surface of the casing.

3. In a multiturn potentiometer having a cylindrical metal housing, the method comprising placing a Wound resistance element in a helix on a cylindrical mandrel, applying a thermosetting adhesive to said helix, applying a sheet of insulating material to said helix, applying thermosetting adhesive to the exterior of said surface, then inserting the mandrel and resulting structure into the cylindrical metal housing, baking said assembly and mandrel and then removing said mandrel.

4. In a multiturn potentiometer having a cylindrical metal housing, the method of improving the linearity and electrical tolerances comprising winding a wire Wound flat resistance element strip in a helix on a helically grooved cylindrical mandrel, applying a thermosetting adhesive to said helix, applying a sheet of insulating mato said helix, applying thermosetting adhesive to the exterior of said insulating material, then inserting the assembly into the cylindrical metal housing, baking said housing and assembly, and then removing said mandrel.

References Cited in the file of this patent UNITED STATES PATENTS 971,101 Van Aller Sept. 27, 1910 1,606,153 Douglas Nov. 9, 1926 2,495,321 Gibbs et al. Ian. 24, 1950 2,558,326 Van Dyke June 26, 1951 2,595,189 Devvan Apr. 29, 1952 2,665,355 Van Alen et al Jan. 5, 1954 

